Shipmen refnum Update allowed property for inbound integration

Summary:

Hi,

We have configured an inbound integration events (shipmentstatus) that inserts new daily events.

We have a problem because we want avoid to update the shipment reference number bellow indicated as (ShipmentRefnumValue) when we receive the inbound message.

Actually we have configured the shipment reference number as Update Allowed = "One,Update" and the refnum is updated:

Bue we are trying to change this property to "One, Don't Update" in order avoid this update the Refnum but unfortunately we get the error bellow:

Can you please help us with this? Is it possible avoid to update the shipment reference number in this case?